Glitter is nearly ubiquitous throughout the world and is used to decorate packaging, clothing, the human body, sporting goods, and many other articles. Glitter, which is a plurality of particles having a regular or irregular periphery, is known in forms that include light reflecting or light refracting material. For example glitter is described in U.S. Pat. No. RE 31,780 (Cooper et al.), U.S. Pat. No. 3,764,067 (Coffey et al.), U.S. Pat. No. 4,310,584 (Cooper et al.), and U.S. Pat. No. 5,294,657 (Melendy et al.).
Materials useful as glitter include particles of metal such as aluminum, copper, silver, gold, brass and particles of transparent or colored, solid organic materials such as poly(ethylene terephthalate), polymethacrylate, and poly(vinylbutyral), and particles of metal coated film or paper (e.g., aluminum coated poly(ethylene terephthalate) film).
Glitter may be clear or may be provided in a variety of colors such as silver, gold, blue, red, etc., or mixtures thereof; and may be provided in a variety of shapes such as circles, squares, rectangles, triangles, diamonds, stars, symbols, alphanumerics (i.e., letters and/or numbers), or mixtures of different shapes.
What is most noticeable about articles coated with glitter is that they tend to glitter or sparkle even when the light source, the coated article and the observer are stationary. Relative movement between the light source, coated article and observer is not required to perceive the glittery appearance of coated articles. Glitter particles each have a large surface area available for reflection, and the glittery effect comes from the misalignment of these particles. However, when relative movement is present, a glitter-coated article tends to sparkle in a dynamic manner wherein the location from where the sparkling effect is viewed, appears to constantly change with movement. Glitter is most noticeable when the glitter particles are opaque; hence, most glitter is formed of an opaque reflective material. Non-opaque glitter particles tend to be faint and washed-out in appearance.
Glitter is commercially available in a variety of colors, shapes and sizes. Since the human eye can barely perceive any glittery effect from reflective particles less than 20 microns in diameter, true glitter particles tend to be larger than 50 microns in diameter. For a pleasing visual effect, it is also preferable for glitter particles to be substantially uniform in shape and size. Having some particles that are too large and significantly larger than other adjacent particles lessens the interesting effect that glitter provides, as the eye tends to focus momentarily on the larger particles distracting the viewer. In contrast, if particles are too small, they simply take up valuable space without providing any perceivable glittery effect.
Metallic appearance of effect pigment has increased rapidly in popularity in the last few years. However, customers are looking for new and exciting visual appearances pushing continuously the research and development of new coatings and applications of paint, inks, gels, etc
Continuous work is ongoing to improve the appearance and performance of coatings. As of late, glitter particles having enhanced new features are desired. By way of example, U.S. Pat. No. 6,475,609 in the name of Whitney et al., incorporated herein by reference, describes a glitter that is made of a large number of alternating layers of a two different organic polymeric materials, wherein at least one of the polymeric materials is birefringent. Although the invention described by Whitney et al. appears to function as intended, the structure is non-opaque and does not provide very high chroma or reflectivity. The color shifting that is provided tends to be within a range of two washed-out appearing colors, thus the overall effect is not particularly striking. Neither the glitter affect nor the color shifting effect is particularly good.
Opaque, inorganic based color shifting Fabry-Perot structures have been used for years and have excellent color shifting visual effects. Typically, structures of this type in the form of foils are made by depositing upon a substrate, a reflector layer, followed by a dielectric layer followed by an absorber layer. These foils appear highly reflective from one side due to the presence of a reflector layer and appear highly reflective with a color that changes in an angle dependent manner when viewed from the opposite side due to the Fabry-Perot structure. Flakes for use in paints and inks can be obtained from symmetric Fabry-Perot structures of the type Abs/Diel/Ref/Diel/Abs, where two single Fabry-Perot structures share the same reflector, by stripping off the deposited layers in the form of flakes from the substrate, and subsequently drying the flakes. These color shifting flakes vary in size from about 2 microns to about 20 microns and can be added to a carrier to make inks or paints which exhibit color shifting effects. A great deal of effort has gone into techniques for achieving a relatively high yield of flakes that are substantially uniform in size, generally less than about 20 microns in diameter. Chromaflair™, is a commercially successful product sold by JDS Uniphase Corporation, wherein these small flakes having an average diameter of about 17 microns are dispersed in a carrier to form paint or ink. This paint has gained popularity and is used to coat vehicles, toys, and various other devices and packaging for its highly attractive appeal.
If one looks very closely at an object coated with Chromaflair™, a glittery appearance can only be faintly discerned and is only barely perceptible. In fact, without straining one's eyes purposefully looking for a glitter effect, it is likely that no glitter effect would be noticed. On the contrary, a strong metallic effect is observed; the predominant effect is the color shifting from the opaque flakes within the carrier. Due to the particle size of flakes used in Chromaflair™ the observer sees a slight iridescence rather than a glitter. Samples of Chromaflair™ may currently be found for viewing on the internet at www.jdsu.com.
In order for these paints and inks to appear truly “glittery” the particles would have to be of a diameter similar to conventional glitter; that is, greater than about 30 microns or more and preferably more than 50 microns and up to or greater than 2000 microns.
As was described heretofore, conventional optically variable (OV) flakes used to make inks and paints are obtained by scraping a foil that has been coated with a symmetric multilayer opaque color shifting film. Prior to scraping, the foil is typically placed in a chemical bath, for example in acetone, so as to loosen the deposited layers from the substrate. During the scraping process the flakes tend to break apart from their carrier substrate in pieces having a large distribution in particle size. Some flakes may have an equivalent diameter of about 1-5 microns while others may have an equivalent diameter of up to 125 microns. Although the large particles are desirous for use as glitter, the size in which particles break cannot be accurately controlled and tend to be too small on average. Furthermore, particles having large diameters tend to curl, losing their ability to serve as high quality glitter which needs to be relatively flat.
In summary it is preferred to have glitter particles which are substantially flat, uniform in size and shape, and which are opaque.
It is also desirous to have glitter particles which are at least 30 microns in size, and which have excellent color shifting qualities and high chroma as well as high reflectivity.
The applicant has found that by using conventional techniques used to make color shifting pigments used in paints or inks, high quality glitter cannot be made as the particle distribution, size and flatness required for glitter cannot be met.
It is therefore an object of this invention to provide glitter which has high chroma, is opaque, and which can be manufactured in a desired shape with a very even size distribution, and wherein the particles are large enough and flat enough to be recognized as glitter.
It is also an object of this invention, to provide a glitter which both provides a strong glitter effect when the object is stationary, and which provides a high degree of chroma and strong color shifting effects when the object or light source upon the object is moved.
It is an object of this invention to provide color shifting glitter particles that have an average size that meets the requirement of glitter, and wherein the particles are substantially flat.
In accordance with this invention, an opaque color-shifting glitter is provided, wherein a structure is provided comprising an organic support layer and; a) a single or double period Fabry-Perot structure on each side of the organic support layer, or, b) two single or a double period Fabry-Perot structure sharing the same reflector layer on one side of an organic support layer or c) an optically variable color shift ink on one side of an organic support layer.
In accordance with this invention these glitter particles preferably each have a diameter “d” of at least 30 microns, and a thickness “t” of more than 6 microns wherein t<d/2. The organic support layer provides rigidity for preventing the color shift coating from curling, for allowing precise cutting of the glitter substrate into discreet particle size and or lessening chipping and breaking of the interference coatings.
In an alternative embodiment, the opaque color shifting glitter is embossed with a diffractive microstructure providing a glitter that shows opaque color shifting by thin film and diffractive light interference simultaneously. This combined interference is disclosed in U.S. Pat. No. 6,841,238 related to chromatic pigments and foils.
An alternative embodiment that is within the scope of this invention is to put one of the above mentioned structures (a), (b) or (c) onto pre-sized substrates that all have the same size i.e. glass flake, mica, boron nitride, aluminum oxide that conform to the above dimensions. This process is disclosed in U.S. Pat. Nos. 6,524,381 and 6,777,085 patent, related to coating particles.
In accordance with an aspect of this invention, an opaque color-shifting glitter is provided, comprising a plurality of glitter particles, wherein the glitter particles each comprise an organic support layer carrying on each side thereof, a reflector layer, a dielectric layer and an absorber layer, said particles each having an diameter “d” of at least 30 microns, and a thickness “t” of more than 6 microns wherein t<d/2, the organic support layer providing rigidity for preventing the particles from curling and for lessening chipping and breaking of the particles.
In accordance with this invention an opaque color shifting glitter is provided comprising glitter particles that have been produced by mechanical means or by a laser inscribing tool such that their shape and size is substantially uniform, said glitter particles each comprising an inorganic thin film optical interference structure providing a perceivable color shift with a change in viewing angle or angle of incident light, in the visible spectrum, wherein said inorganic thin film interference structure of each particle is supported by an organic support layer for providing rigidity and for preventing the particles from curling.